NEW YORK — How can a cancer come back after it’s apparently been eradicated?
Three new studies are bolstering a long-debated idea: that tumors contain their
own pool of stem cells that can multiply and keep fueling the cancer, seeding
regrowth.

If that’s true, scientists will need to find a way to kill those cells, apart
from how they attack the rest of the tumor.

Stem cells in healthy tissues are known for their ability to produce any kind
of cell. The new research deals with a different kind, cancer stem cells. Some
researchers, but not all, believe they lurk as a persisting feature in tumors.

Over the past decade, studies have found evidence for them in tumors such as
breast and colon cancers. But this research has largely depended on
transplanting human cancer cells into mice that don’t have immune systems, an
artificial environment that raises questions about the relevance of the results.

Now, three studies reported online Wednesday in the journals Nature and Science present evidence for cancer stem cells within the
original tumors. Again, the research relies on mice. That and other factors mean
the new findings still won’t convince everyone that cancer stem cells are key to
finding more powerful treatments.

But researcher Luis Parada, of the University of Texas Southwestern Medical
Center in Dallas, believes his team is onto something. He says that for the type
of brain tumor his team studied, “we’ve identified the true enemy.”

If his finding applies to other cancers, he said, then even if chemotherapy
drastically shrinks a tumor but doesn’t affect its supply of cancer stem cells,
“very little progress has actually been made.”

The three studies used labeling techniques to trace the ancestry of cells
within mouse tumors.

Collectively, they give “very strong support” to the cancer stem cell theory,
said Jeffrey M. Rosen, a professor of molecular and cellular biology at Baylor
College of Medicine in Houston. He did not participate in the work but supports
the theory, which he said is widely accepted.

Parada’s study appears in Nature. In a second Nature report, British and Belgian researchers found
evidence for cancer stem cells in early stage skin tumors in mice. And in the
journal Science, a Dutch group found such evidence in mouse
intestinal polyps, which are precursors to colon cancer.

Scott Kern of the Sidney Kimmel Comprehensive Cancer Center at Johns Hopkins
University in Baltimore is skeptical about whether tumors contain cancer stem
cells. He said that since the new studies didn’t involve human tumors, it’s not
clear how relevant they are to people.

The two European studies focused largely on lesions that can lead to tumors,
he said. And as for Parada’s brain cancer study, he said he believed the results
could be explained without relying on the cancer stem cell theory.